<!--{
	"Title": "Go 1.17 Release Notes",
	"Path":  "/doc/go1.17"
}-->

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<h2 id="introduction">DRAFT RELEASE NOTES — Introduction to Go 1.17</h2>

<p>
  <strong>
    Go 1.17 is not yet released. These are work-in-progress
    release notes. Go 1.17 is expected to be released in August 2021.
  </strong>
</p>

<h2 id="language">Changes to the language</h2>

<p>
  Go 1.17 includes three small enhancements to the language.
</p>

<ul>
  <li><!-- CL 216424; issue 395 -->
    <a href="/ref/spec#Conversions_from_slice_to_array_pointer">Conversions
    from slice to array pointer</a>: An expression <code>s</code> of
    type <code>[]T</code> may now be converted to array pointer type
    <code>*[N]T</code>. If <code>a</code> is the result of such a
    conversion, then corresponding indices that are in range refer to
    the same underlying elements: <code>&amp;a[i] == &amp;s[i]</code>
    for <code>0 &lt;= i &lt; N</code>. The conversion panics if
    <code>len(s)</code> is less than <code>N</code>.
  </li>

  <li><!-- CL 312212; issue 40481 -->
    <a href="/pkg/unsafe#Add"><code>unsafe.Add</code></a>:
    <code>unsafe.Add(ptr, len)</code> adds <code>len</code>
    to <code>ptr</code> and returns the updated pointer
    <code>unsafe.Pointer(uintptr(ptr) + uintptr(len))</code>.
  </li>

  <li><!-- CL 312212; issue 19367 -->
    <a href="/pkg/unsafe#Slice"><code>unsafe.Slice</code></a>:
    For expression <code>ptr</code> of type <code>*T</code>,
    <code>unsafe.Slice(ptr, len)</code> returns a slice of
    type <code>[]T</code> whose underlying array starts
    at <code>ptr</code> and whose length and capacity
    are <code>len</code>.
  </li>
</ul>

<p>
  These enhancements were added to simplify writing code that conforms
  to <code>unsafe.Pointer</code>'s <a href="/pkg/unsafe/#Pointer">safety
  rules</a>, but the rules remain unchanged. In particular, existing
  programs that correctly use <code>unsafe.Pointer</code> remain
  valid, and new programs must still follow the rules when
  using <code>unsafe.Add</code> or <code>unsafe.Slice</code>.
</p>

<h2 id="ports">Ports</h2>

<h3 id="darwin">Darwin</h3>

<p><!-- golang.org/issue/23011 -->
  As <a href="go1.16#darwin">announced</a> in the Go 1.16 release
  notes, Go 1.17 requires macOS 10.13 High Sierra or later; support
  for previous versions has been discontinued.
</p>

<h3 id="windows">Windows</h3>

<p><!-- golang.org/issue/36439 -->
  Go 1.17 adds support of 64-bit ARM architecture on Windows (the
  <code>windows/arm64</code> port). This port supports cgo.
</p>

<h3 id="openbsd">OpenBSD</h3>

<p><!-- golang.org/issue/43005 -->
  The 64-bit MIPS architecture on OpenBSD (the <code>openbsd/mips64</code>
  port) now supports cgo.
</p>

<p><!-- golang.org/issue/36435 -->
  In Go 1.16, on the 64-bit x86 and 64-bit ARM architectures on
  OpenBSD (the <code>openbsd/amd64</code> and <code>openbsd/arm64</code>
  ports) system calls are made through <code>libc</code>, instead
  of directly using the machine instructions. In Go 1.17, this is
  also done on the 32-bit x86 and 32-bit ARM architectures on OpenBSD
  (the <code>openbsd/386</code> and <code>openbsd/arm</code> ports).
  This ensures forward-compatibility with future versions of
  OpenBSD.
</p>

<h3 id="arm64">ARM64</h3>

<p><!-- CL 288814 -->
  Go programs now maintain stack frame pointers on the 64-bit ARM
  architecture on all operating systems. Previously it maintained
  stack frame pointers only on Linux, macOS, and iOS.
</p>

<p>
  TODO: complete the Ports section
</p>

<h2 id="tools">Tools</h2>

<p>
  TODO: complete the Tools section
</p>

<h3 id="go-command">Go command</h3>

<h4 id="lazy-loading">Lazy module loading</h4>

<p><!-- golang.org/issue/36460 -->
  If a module specifies <code>go</code> <code>1.17</code> or higher in its
  <code>go.mod</code> file, its transitive requirements are now loaded lazily,
  avoiding the need to download or read <code>go.mod</code> files for
  otherwise-irrelevant dependencies. To support lazy loading, in Go 1.17 modules
  the <code>go</code> command maintains <em>explicit</em> requirements in
  the <code>go.mod</code> file for every dependency that provides any package
  transitively imported by any package or test within the module.
  See <a href="https://golang.org/design/36460-lazy-module-loading">the design
  document</a> for more detail.
  <!-- TODO(bcmills): replace the design-doc link with proper documentation. -->
</p>

<p><!-- golang.org/issue/45094 --> To facilitate the upgrade to lazy loading,
  the <code>go</code> <code>mod</code> <code>tidy</code> subcommand now supports
  a <code>-go</code> flag to set or change the <code>go</code> version in
  the <code>go.mod</code> file. To enable lazy loading for an existing module
  without changing the selected versions of its dependencies, run:
</p>

<pre>
  go mod tidy -go=1.17
</pre>

<p><!-- golang.org/issue/46141 -->
  TODO: Describe the <code>-compat</code> flag
  for <code>go</code> <code>mod</code> <code>tidy</code>.
</p>

<h4 id="module-deprecation-comments">Module deprecation comments</h4>

<p><!-- golang.org/issue/40357 -->
  Module authors may deprecate a module by adding a
  <a href="/ref/mod#go-mod-file-module-deprecation"><code>// Deprecated:</code>
  comment</a> to <code>go.mod</code>, then tagging a new version.
  <code>go</code> <code>get</code> now prints a warning if a module needed to
  build packages named on the command line is deprecated. <code>go</code>
  <code>list</code> <code>-m</code> <code>-u</code> prints deprecations for all
  dependencies (use <code>-f</code> or <code>-json</code> to show the full
  message). The <code>go</code> command considers different major versions to
  be distinct modules, so this mechanism may be used, for example, to provide
  users with migration instructions for a new major version.
</p>

<h4 id="go-get"><code>go</code> <code>get</code></h4>

<p><!-- golang.org/issue/37519 -->
  The <code>go</code> <code>get</code> <code>-insecure</code> flag is
  deprecated and has been removed. To permit the use of insecure schemes
  when fetching dependencies, please use the <code>GOINSECURE</code>
  environment variable. The <code>-insecure</code> flag also bypassed module
  sum validation, use <code>GOPRIVATE</code> or <code>GONOSUMDB</code> if
  you need that functionality. See <code>go</code> <code>help</code>
  <code>environment</code> for details.
</p>

<h4 id="missing-go-directive"><code>go.mod</code> files missing <code>go</code> directives</h4>

<p><!-- golang.org/issue/44976 -->
  If the main module's <code>go.mod</code> file does not contain
  a <a href="/doc/modules/gomod-ref#go"><code>go</code> directive</a> and
  the <code>go</code> command cannot update the <code>go.mod</code> file, the
  <code>go</code> command now assumes <code>go 1.11</code> instead of the
  current release. (<code>go</code> <code>mod</code> <code>init</code> has added
  <code>go</code> directives automatically <a href="/doc/go1.12#modules">since
  Go 1.12</a>.)
</p>

<p><!-- golang.org/issue/44976 -->
  If a module dependency lacks an explicit <code>go.mod</code> file, or
  its <code>go.mod</code> file does not contain
  a <a href="/doc/modules/gomod-ref#go"><code>go</code> directive</a>,
  the <code>go</code> command now assumes <code>go 1.16</code> for that
  dependency instead of the current release. (Dependencies developed in GOPATH
  mode may lack a <code>go.mod</code> file, and
  the <code>vendor/modules.txt</code> has to date never recorded
  the <code>go</code> versions indicated by dependencies' <code>go.mod</code>
  files.)
</p>

<h4 id="vendor"><code>vendor</code> contents</h4>

<p><!-- golang.org/issue/36876 -->
  If the main module specifies <code>go</code> <code>1.17</code> or higher,
  <code>go</code> <code>mod</code> <code>vendor</code> now annotates
  <code>vendor/modules.txt</code> with the <code>go</code> version indicated by
  each vendored module in its own <code>go.mod</code> file. The annotated
  version is used when building the module's packages from vendored source code.
</p>

<p><!-- golang.org/issue/42970 -->
  If the main module specifies <code>go</code> <code>1.17</code> or higher,
  <code>go</code> <code>mod</code> <code>vendor</code> now omits <code>go.mod</code>
  and <code>go.sum</code> files for vendored dependencies, which can otherwise
  interfere with the ability of the <code>go</code> command to identify the correct
  module root when invoked within the <code>vendor</code> tree.
</p>

<h4 id="password-prompts">Password prompts</h4>

<p><!-- golang.org/issue/44904 -->
  The <code>go</code> command by default now suppresses SSH password prompts and
  Git Credential Manager prompts when fetching Git repositories using SSH, as it
  already did previously for other Git password prompts. Users authenticating to
  private Git repos with password-protected SSH may configure
  an <code>ssh-agent</code> to enable the <code>go</code> command to use
  password-protected SSH keys.
</p>

<h4 id="go-mod-download"><code>go</code> <code>mod</code> <code>download</code></h4>

<p><!-- golang.org/issue/45332 -->
  When <code>go</code> <code>mod</code> <code>download</code> is invoked without
  arguments, it will no longer save sums for downloaded module content to
  <code>go.sum</code>. It may still make changes to <code>go.mod</code> and
  <code>go.sum</code> needed to load the build list. This is the same as the
  behavior in Go 1.15. To save sums for all modules, use <code>go</code>
  <code>mod</code> <code>download</code> <code>all</code>.
</p>

<p><!-- CL 249759 -->
  TODO: <a href="https://golang.org/cl/249759">https://golang.org/cl/249759</a>: cmd/cover: replace code using optimized golang.org/x/tools/cover
</p>

<h3 id="vet">Vet</h3>

<p><!-- CL 299532 -->
  TODO: <a href="https://golang.org/cl/299532">https://golang.org/cl/299532</a>: cmd/vet: bring in sigchanyzer to report unbuffered channels to signal.Notify
</p>

<p>
  TODO: complete the Vet section
</p>

<h2 id="compiler">Compiler</h2>

<p><!-- golang.org/issue/40724 -->
  Go 1.17 implements a new way of passing function arguments and results using
  registers instead of the stack. This work is enabled for Linux, MacOS, and
  Windows on the 64-bit x86 architecture (the <code>linux/amd64</code>,
  <code>darwin/amd64</code>, <code>windows/amd64</code> ports). For a
  representative set of Go  packages and programs, benchmarking has shown
  performance improvements of about 5%, and a typical reduction in binary size
  of about 2%.
</p>

<p>
  This change does not affect the functionality of any safe Go code. It can affect
  code outside the <a href="/doc/go1compat">compatibility guidelines</a> with
  minimal impact. To maintain compatibility with existing assembly functions,
  adapter functions converting between the new register-based calling convention
  and the previous stack-based calling convention (also known as ABI wrappers)
  are sometimes used. This is mostly invisible to users, except for assembly
  functions that have their addresses taken in Go. Using <code>reflect.ValueOf(fn).Pointer()</code>
  (or similar approaches such as via <code>unsafe.Pointer</code>) to get the address
  of an assembly function will now return the address of the ABI wrapper. This is
  mostly harmless, except for special-purpose assembly code (such as accessing
  thread-local storage or requiring a special stack alignment). Assembly functions
  called indirectly from Go via <code>func</code> values will now be made through
  ABI wrappers, which may cause a very small performance overhead. Also, calling
  Go functions from assembly may now go through ABI wrappers, with a very small
  performance overhead.
</p>

<p><!-- CL 304470 -->
  The format of stack traces from the runtime (printed when an uncaught panic
  occurs, or when <code>runtime.Stack</code> is called) is improved. Previously,
  the function arguments were printed as hexadecimal words based on the memory
  layout. Now each argument in the source code is printed separately, separated
  by commas. Aggregate-typed (struct, array, string, slice, interface, and complex)
  arguments are delimited by curly braces. A caveat is that the value of an
  argument that only lives in a register and is not stored to memory may be
  inaccurate. Results (which were usually inaccurate) are no longer printed.
</p>

<p><!-- CL 283112, golang.org/issue/28727 -->
  Functions containing closures can now be inlined. One effect of this change is
  that a function with a closure may actually produce a distinct closure function
  for each place that the function is inlined. Hence, this change could reveal
  bugs where Go functions are compared (incorrectly) by pointer value. Go
  functions are by definition not comparable.
</p>

<h2 id="library">Core library</h2>

<p>
  TODO: complete the Core library section
</p>

<h3 id="crypto/tls"><a href="/pkg/crypto/tls">crypto/tls</a></h3>

<p><!-- CL 295370 -->
  <a href="/pkg/crypto/tls#Conn.HandshakeContext">(*Conn).HandshakeContext</a> was added to
  allow the user to control cancellation of an in-progress TLS Handshake.
  The context provided is propagated into the
  <a href="/pkg/crypto/tls#ClientHelloInfo">ClientHelloInfo</a>
  and <a href="/pkg/crypto/tls#CertificateRequestInfo">CertificateRequestInfo</a>
  structs and accessible through the new
  <a href="/pkg/crypto/tls#ClientHelloInfo.Context">(*ClientHelloInfo).Context</a>
  and
  <a href="/pkg/crypto/tls#CertificateRequestInfo.Context">
      (*CertificateRequestInfo).Context
  </a> methods respectively. Canceling the context after the handshake has finished
  has no effect.
</p>

<p><!-- CL 289209 -->
  When <a href="/pkg/crypto/tls#Config">Config.NextProtos</a> is set, servers now
  enforce that there is an overlap between the configured protocols and the protocols
  advertised by the client, if any. If there is no overlap the connection is closed
  with the <code>no_application_protocol</code> alert, as required by RFC 7301.
</p>

<h3 id="runtime/cgo"><a href="/pkg/runtime/cgo">Cgo</a></h3>

<p>
  The <a href="/pkg/runtime/cgo">runtime/cgo</a> package now provides a
  new facility that allows to turn any Go values to a safe representation
  that can be used to pass values between C and Go safely. See
  <a href="/pkg/runtime/cgo#Handle">runtime/cgo.Handle</a> for more information.
</p>

<h3 id="minor_library_changes">Minor changes to the library</h3>

<p>
  As always, there are various minor changes and updates to the library,
  made with the Go 1 <a href="/doc/go1compat">promise of compatibility</a>
  in mind.
</p>

<dl id="archive/zip"><dt><a href="/pkg/archive/zip/">archive/zip</a></dt>
  <dd>
    <p><!-- CL 312310 -->
      The new methods <a href="/pkg/archive/zip#File.OpenRaw"><code>File.OpenRaw</code></a>, <a href="/pkg/archive/zip#Writer.CreateRaw"><code>Writer.CreateRaw</code></a>, <a href="/pkg/archive/zip#Writer.Copy"><code>Writer.Copy</code></a> provide support for cases where performance is a primary concern.
    </p>
  </dd>
</dl><!-- archive/zip -->

<dl id="bufio"><dt><a href="/pkg/bufio/">bufio</a></dt>
  <dd>
    <p><!-- CL 280492 -->
      The <a href="/pkg/bufio/#Writer.WriteRune"><code>Writer.WriteRune</code></a> method
      now writes the replacement character U+FFFD for negative rune values,
      as it does for other invalid runes.
    </p>
  </dd>
</dl><!-- bufio -->

<dl id="bytes"><dt><a href="/pkg/bytes/">bytes</a></dt>
  <dd>
    <p><!-- CL 280492 -->
      The <a href="/pkg/bytes/#Buffer.WriteRune"><code>Buffer.WriteRune</code></a> method
      now writes the replacement character U+FFFD for negative rune values,
      as it does for other invalid runes.
    </p>
  </dd>
</dl><!-- bytes -->

<dl id="compress/lzw"><dt><a href="/pkg/compress/lzw/">compress/lzw</a></dt>
  <dd>
    <p><!-- CL 273667 -->
      The <a href="/pkg/compress/lzw/#NewReader"><code>NewReader</code></a>
      function is guaranteed to return a value of the new
      type <a href="/pkg/compress/lzw/#Reader"><code>Reader</code></a>,
      and similarly <a href="/pkg/compress/lzw/#NewWriter"><code>NewWriter</code></a>
      is guaranteed to return a value of the new
      type <a href="/pkg/compress/lzw/#Writer"><code>Writer</code></a>.
      These new types both implement a <code>Reset</code> method
      (<a href="/pkg/compress/lzw/#Reader.Reset"><code>Reader.Reset</code></a>,
      <a href="/pkg/compress/lzw/#Writer.Reset"><code>Writer.Reset</code></a>)
      that allows reuse of the <code>Reader</code> or <code>Writer</code>.
    </p>
  </dd>
</dl><!-- compress/lzw -->

<dl id="crypto/rsa"><dt><a href="/pkg/crypto/rsa/">crypto/rsa</a></dt>
  <dd>
    <p><!-- CL 302230 -->
      TODO: <a href="https://golang.org/cl/302230">https://golang.org/cl/302230</a>: fix salt length calculation with PSSSaltLengthAuto
    </p>
  </dd>
</dl><!-- crypto/rsa -->

<dl id="database/sql"><dt><a href="/pkg/database/sql/">database/sql</a></dt>
  <dd>
    <p><!-- CL 258360 -->
      The <a href="/pkg/database/sql/#DB.Close"><code>DB.Close</code></a> method now closes
      the <code>connector</code> field if the type in this field implements the
      <a href="/pkg/io/#Closer"><code>io.Closer</code></a> interface.
    </p>

    <p><!-- CL 311572 -->
      The new
      <a href="/pkg/database/sql/#NullInt16"><code>NullInt16</code></a> 
      and 
      <a href="/pkg/database/sql/#NullByte"><code>NullByte</code></a> 
      structs represent the int16 and byte values that may be null. These can be used as
      destinations of the <a href="/pkg/database/sql/#Scan"><code>Scan</code></a> method,
      similar to NullString.
    </p>
  </dd>
</dl><!-- database/sql -->

<dl id="debug/elf"><dt><a href="/pkg/debug/elf/">debug/elf</a></dt>
  <dd>
    <p><!-- CL 239217 -->
      The <a href="/pkg/debug/elf/#SHT_MIPS_ABIFLAGS"><code>SHT_MIPS_ABIFLAGS</code></a>
      constant has been added.
    </p>
  </dd>
</dl><!-- debug/elf -->

<dl id="encoding/binary"><dt><a href="/pkg/encoding/binary/">encoding/binary</a></dt>
  <dd>
    <p><!-- CL 299531 -->
      <code>binary.Uvarint</code> will stop reading after <code>10 bytes</code> to avoid
      wasted computations. If more than <code>10 bytes</code> are needed, the byte count returned is <code>-11</code>.
      <br />
      Previous Go versions could return larger negative counts when reading incorrectly encoded varints.
    </p>
  </dd>
</dl><!-- encoding/binary -->

<dl id="encoding/csv"><dt><a href="/pkg/encoding/csv/">encoding/csv</a></dt>
  <dd>
    <p><!-- CL 291290 -->
      The new
      <a href="/pkg/encoding/csv/#Reader.FieldPos"><code>Reader.FieldPos</code></a>
      method returns the line and column corresponding to the start of
      a given field in the record most recently returned by
      <a href="/pkg/encoding/csv/#Reader.Read"><code>Read</code></a>.
    </p>
  </dd>
</dl><!-- encoding/csv -->

<dl id="flag"><dt><a href="/pkg/flag/">flag</a></dt>
  <dd>
    <p><!-- CL 271788 -->
      Flag declarations now panic if an invalid name is specified.
    </p>
  </dd>
</dl><!-- flag -->

<dl id="go/build"><dt><a href="/pkg/go/build/">go/build</a></dt>
  <dd>
    <p><!-- CL 310732 -->
      The new
      <a href="/pkg/go/build/#Context.ToolTags"><code>Context.ToolTags</code></a>
      field holds the build tags appropriate to the current Go
      toolchain configuration.
    </p>
  </dd>
</dl><!-- go/build -->

<dl id="io/fs"><dt><a href="/pkg/io/fs/">io/fs</a></dt>
  <dd>
    <p><!-- CL 293649 -->
      The new <a href="/pkg/io/fs/#FileInfoToDirEntry"><code>FileInfoToDirEntry</code></a> function converts a <code>FileInfo</code> to a <code>DirEntry</code>.
    </p>
  </dd>
</dl><!-- io/fs -->

<dl id="math"><dt><a href="/pkg/math/">math</a></dt>
  <dd>
    <p><!-- CL 247058 -->
      The math package now defines three more constants: <code>MaxUint</code>, <code>MaxInt</code> and <code>MinInt</code>.
      For 32-bit systems their values are <code>2^32 - 1</code>, <code>2^31 - 1</code> and <code>-2^31</code>, respectively.
      For 64-bit systems their values are <code>2^64 - 1</code>, <code>2^63 - 1</code> and <code>-2^63</code>, respectively.
    </p>
  </dd>
</dl><!-- math -->

<dl id="mime"><dt><a href="/pkg/mime/">mime</a></dt>
  <dd>
    <p><!-- CL 305230 -->
      On Unix systems, the table of MIME types is now read from the local system's
      <a href="https://specifications.freedesktop.org/shared-mime-info-spec/shared-mime-info-spec-0.21.html">Shared MIME-info Database</a>
      when available.
    </p>
  </dd>
</dl><!-- mime -->

<dl id="net"><dt><a href="/pkg/net/">net</a></dt>
  <dd>
    <p><!-- CL 272668 -->
      The new method <a href="/pkg/net/#IP.IsPrivate"><code>IP.IsPrivate</code></a> reports whether an address is
      a private IPv4 address according to <a href="http://tools.ietf.org/html/rfc1918">RFC 1918</a>
      or a local IPv6 address according <a href="http://tools.ietf.org/html/rfc4193">RFC 4193</a>.
    </p>

    <p><!-- CL 301709 -->
      The Go DNS resolver now only sends one DNS query when resolving an address for an IPv4-only or IPv6-only network,
      rather than querying for both address families.
    </p>

    <p><!-- CL 307030 -->
      The <a href="/pkg/net/#ErrClosed"><code>ErrClosed</code></a> sentinel error and
      <a href="/pkg/net/#ParseError"><code>ParseError</code></a> error type now implement
      the <a href="/pkg/net/#Error"><code>net.Error</code></a> interface.
    </p>
  </dd>
</dl><!-- net -->

<dl id="net/http"><dt><a href="/pkg/net/http/">net/http</a></dt>
  <dd>
    <p><!-- CL 295370 -->
      The <a href="/pkg/net/http/"><code>net/http</code></a> package now uses the new
      <a href="/pkg/crypto/tls#Conn.HandshakeContext"><code>(*tls.Conn).HandshakeContext</code></a>
      with the <a href="/pkg/net/http/#Request"><code>Request</code></a> context
      when performing TLS handshakes in the client or server.
    </p>

    <p><!-- CL 235437 -->
      Setting the <a href="/pkg/net/http/#Server"><code>Server</code></a>
      <code>ReadTimeout</code> or <code>WriteTimeout</code> fields to a negative value now indicates no timeout
      rather than an immediate timeout.
    </p>

    <p><!-- CL 308952 -->
      The <a href="/pkg/net/http/#ReadRequest"><code>ReadRequest</code></a> function
      now returns an error when the request has multiple Host headers.
    </p>
  </dd>
</dl><!-- net/http -->

<dl id="net/http/httptest"><dt><a href="/pkg/net/http/httptest/">net/http/httptest</a></dt>
  <dd>
    <p><!-- CL 308950 -->
      <a href="/pkg/net/http/httptest/#ResponseRecorder.WriteHeader"><code>ResponseRecorder.WriteHeader></code></a>
      now panics when the provided code is not a valid three-digit HTTP status code.
      This matches the behavior of <a href="/pkg/net/http/#ResponseWriter"><code>ResponseWriter></code></a>
      implementations in the <a href="/pkg/net/http/"><code>net/http</code></a> package.
    </p>
  </dd>
</dl><!-- net/http/httptest -->

<dl id="net/url"><dt><a href="/pkg/net/url/">net/url</a></dt>
  <dd>
    <p><!-- CL 314850 -->
      The new method <a href="/pkg/net/url/#Values.Has"><code>Values.Has</code></a>
      reports whether a query parameter is set.
    </p>
  </dd>
</dl><!-- net/url -->

<dl id="os"><dt><a href="/pkg/os/">os</a></dt>
  <dd>
    <p><!-- CL 268020 -->
      The <a href="/pkg/os/#File.WriteString"><code>File.WriteString</code></a> method
      has been optimized to no longer make a copy of the input string.
    </p>
  </dd>
</dl><!-- os -->

<dl id="reflect"><dt><a href="/pkg/reflect/">reflect</a></dt>
  <dd>
    <p><!-- CL 266197 -->
      The new
      <a href="/pkg/reflect/#StructField.IsExported"><code>StructField.IsExported</code></a>
      and
      <a href="/pkg/reflect/#Method.IsExported"><code>Method.IsExported</code></a>
      methods report whether a struct field or type method is exported.
      They provide a more readable alternative to checking whether <code>PkgPath</code>
      is empty.
    </p>

    <p><!-- CL 281233 -->
      The new <a href="/pkg/reflect/#VisibleFields"><code>VisibleFields</code></a> function
      returns all the visible fields in a struct type, including fields inside anonymous struct members.
    </p>

    <p><!-- CL 284136 -->
      The <a href="/pkg/reflect/#ArrayOf"><code>ArrayOf</code></a> function now panics when
      called with a negative length.
    </p>
  </dd>
</dl><!-- reflect -->

<dl id="runtime/metrics"><dt><a href="/pkg/runtime/metrics">runtime/metrics</a></dt>
  <dd>
    <p><!-- CL 308933, CL 312431, CL 312909 -->
      New metrics were added that track total bytes and objects allocated and freed.
      A new metric tracking the distribution of goroutine scheduling latencies was
      also added.
    </p>
  </dd>
</dl><!-- runtime/metrics -->

<dl id="strconv"><dt><a href="/pkg/strconv/">strconv</a></dt>
  <dd>
    <p><!-- CL 170079 -->
      TODO: <a href="https://golang.org/cl/170079">https://golang.org/cl/170079</a>: implement Ryū-like algorithm for fixed precision ftoa
    </p>

    <p><!-- CL 170080 -->
      TODO: <a href="https://golang.org/cl/170080">https://golang.org/cl/170080</a>: Implement Ryū algorithm for ftoa shortest mode
    </p>

    <p><!-- CL 314775 -->
      The new <a href="/pkg/strconv/#QuotedPrefix"><code>QuotedPrefix</code></a> function
      returns the quoted string (as understood by
      <a href="/pkg/strconv/#Unquote"><code>Unquote</code></a>)
      at the start of input.
    </p>
  </dd>
</dl><!-- strconv -->

<dl id="strings"><dt><a href="/pkg/strings/">strings</a></dt>
  <dd>
    <p><!-- CL 280492 -->
      The <a href="/pkg/strings/#Builder.WriteRune"><code>Builder.WriteRune</code></a> method
      now writes the replacement character U+FFFD for negative rune values,
      as it does for other invalid runes.
    </p>
  </dd>
</dl><!-- strings -->

<dl id="sync/atomic"><dt><a href="/pkg/sync/atomic/">sync/atomic</a></dt>
  <dd>
    <p><!-- CL 241678 -->
      <code>atomic.Value</code> now has <a href="/pkg/sync/atomic/#Value.Swap"><code>Swap</code></a> and
      <a href="/pkg/sync/atomic/#Value.CompareAndSwap"><code>CompareAndSwap</code></a> methods that provide
      additional atomic operations.
    </p>
  </dd>
</dl><!-- sync/atomic -->

<dl id="syscall"><dt><a href="/pkg/syscall/">syscall</a></dt>
  <dd>
    <p><!-- CL 295371 -->
    <p>
      The <a href="/pkg/syscall/#GetQueuedCompletionStatus"><code>GetQueuedCompletionStatus</code></a> and
      <a href="/pkg/syscall/#PostQueuedCompletionStatus"><code>PostQueuedCompletionStatus</code></a>
      functions are now deprecated. These functions have incorrect signatures and are superseded by
      equivalents in the <a href="https://godoc.org/golang.org/x/sys/windows"><code>golang.org/x/sys/windows</code></a> package.
    </p>

    <p><!-- CL 313653 -->
      On Unix-like systems, the process group of a child process is now set with signals blocked.
      This avoids sending a <code>SIGTTOU</code> to the child when the parent is in a background process group.
    </p>

    <p><!-- CL 288298, CL 288300 -->
      The Windows version of
      <a href="/pkg/syscall/#SysProcAttr"><code>SysProcAttr</code></a>
      has two new fields. <code>AdditionalInheritedHandles</code> is
      a list of additional handles to be inherited by the new child
      process. <code>ParentProcess</code> permits specifying the
      parent process of the new process.

    <p><!-- CL 311570 -->
      The constant <code>MSG_CMSG_CLOEXEC</code> is now defined on
      DragonFly and all OpenBSD systems (it was already defined on
      some OpenBSD systems and all FreeBSD, NetBSD, and Linux systems).
    </p>

    <p><!-- CL 315281 -->
      The constants <code>SYS_WAIT6</code> and <code>WEXITED</code>
      are now defined on NetBSD systems (<code>SYS_WAIT6</code> was
      already defined on DragonFly and FreeBSD systems;
      <code>WEXITED</code> was already defined on Darwin, DragonFly,
      FreeBSD, Linux, and Solaris systems).
    </p>
  </dd>
</dl><!-- syscall -->

<dl id="testing"><dt><a href="/pkg/testing/">testing</a></dt>
  <dd>
    <p><!-- CL 310033 -->
      Added a new <a href="/cmd/go/#hdr-Testing_flags">testing flag</a> <code>-shuffle</code> which controls the execution order of tests and benchmarks.
    </p>
    <p><!-- CL 260577 -->
      The new
      <a href="/pkg/testing/#T.Setenv"><code>T.Setenv</code></a>
      and <a href="/pkg/testing/#B.Setenv"><code>B.Setenv</code></a>
      methods support setting an environment variable for the duration
      of the test or benchmark.
    </p>
  </dd>
</dl><!-- testing -->

<dl id="text/template/parse"><dt><a href="/pkg/text/template/parse/">text/template/parse</a></dt>
  <dd>
    <p><!-- CL 301493 -->
      The new <a href="/pkg/text/template/parse/#Mode"><code>SkipFuncCheck</code></a> <a href=><code>Mode</code></a>
      value changes the template parser to not verify that functions are defined.
    </p>
  </dd>
</dl><!-- text/template/parse -->

<dl id="time"><dt><a href="/pkg/time/">time</a></dt>
  <dd>
    <p><!-- CL 260858 -->
      The <a href="/pkg/time/#Time"><code>Time</code></a> type now has a
      <a href="/pkg/time/#Time.GoString"><code>GoString</code></a> method that
      will return a more useful value for times when printed with the
      <code>%#v</code> format specifier in the <code>fmt</code> package.
    </p>

    <p><!-- CL 264077 -->
      The new <a href="/pkg/time/#Time.IsDST"><code>Time.IsDST</code></a> method can be used to check whether the time
      is in Daylight Savings Time in its configured location.
    </p>

    <p><!-- CL 293349 -->
      The new <a href="/pkg/time/#Time.UnixMilli"><code>Time.UnixMilli</code></a> and
      <a href="/pkg/time/#Time.UnixMicro"><code>Time.UnixMicro</code></a> methods return the number of milliseconds and
      microseconds elapsed since January 1, 1970 UTC respectively.<br>
      The new <code>UnixMilli</code> and <code>UnixMicro</code> functions return local Time corresponding to given
      Unix time.
    </p>

    <p><!-- CL 300996 -->
      The package now accepts comma "," as a separator for fractional seconds when parsing and formatting time.
      The following time formats are now accepted:
      <ul>
        <li>2006-01-02 14:06:03,999999999 -0700 MST</li>
        <li>Mon Jan _2 14:06:03,120007 2006</li>
        <li>Mon Jan 2 14:06:03,120007 2006</li>
      </ul>
    </p>

    <p><!-- CL 320252 -->
      The new constant <a href="/pkg/time/#Layout"><code>Layout</code></a>
      defines the reference time.
    </p>
  </dd>
</dl><!-- time -->

<dl id="unicode"><dt><a href="/pkg/unicode/">unicode</a></dt>
  <dd>
    <p><!-- CL 280493 -->
      The <a href="/pkg/unicode/#Is"><code>Is</code></a>,
      <a href="/pkg/unicode/#IsGraphic"><code>IsGraphic</code></a>,
      <a href="/pkg/unicode/#IsLetter"><code>IsLetter</code></a>,
      <a href="/pkg/unicode/#IsLower"><code>IsLower</code></a>,
      <a href="/pkg/unicode/#IsMark"><code>IsMark</code></a>,
      <a href="/pkg/unicode/#IsNumber"><code>IsNumber</code></a>,
      <a href="/pkg/unicode/#IsPrint"><code>IsPrint</code></a>,
      <a href="/pkg/unicode/#IsPunct"><code>IsPunct</code></a>,
      <a href="/pkg/unicode/#IsSpace"><code>IsSpace</code></a>,
      <a href="/pkg/unicode/#IsSymbol"><code>IsSymbol</code></a>, and
      <a href="/pkg/unicode/#IsUpper"><code>IsUpper</code></a> functions
      now return <code>false</code> on negative rune values, as they do for other invalid runes.
    </p>
  </dd>
</dl><!-- unicode -->
